I think now is a good time to remind you all that what we saw and heard about the Vishnans in AoA was all just how they portrayed themselves to Sam. It might not be wise to take them at face value or trust them so readily....
Considering how powerful the Shivans are, how extant they are, and how vulnerable the GTVA would still remain well into the future, I'd definitely put my lot in with the guys who by and large helped us out many times in a row in big ways, and went through a lot of effort to act largely benevolently for a bunch of relative strangers. They even defended terrans and vasudans (morally/politically/militarily) in a direct and pivotal confrontation with the Shivans. And they seem to be the only race capable of fully matching the Shivans.
So sure, I don't exactly trust them all that much, but given the situation, being a valuable pawn with the protection of several queens is much more preferable to being a lone knight against several queens. While it's technically possible that the Vishnans were deceiving us all along, all consequences and direct evidence be damned, I still rather doubt that the Vishnans have particularly bad and strict goals in mind for the terran and vasudan races.
Maybe the Vishnans have an Assimilation Plot in mind for the allied races--making them into a new, non-artificial subspace stack entity to fulfill the role of the Brahmans of old. Assuming that this is not a desirable outcome, it seems like it would still be dependent on the GTVA population being willing and ready for the process in the first place. I obviously don't know with any kind of certainty, but the Vishnans don't seem to be the type to force "enlightenment" on a race that believes itself to not be "ready" for something like that.
Besides, if the GTVA/Tev leadership believes itself incapable of checking the potential spread and growth of Ubuntu culture, even with the invincible and overt points of the Second Shivan Incursion/Capella and whatever evidence the Tev government has on the dangers of "enlightenment"/being highly obedient to the Vishnans, then Tev culture absolutely
sucks, along with its seeming lack of adaptability, common sense (Let relations between terrans and vasudans whither to cold, barely friendly levels--
even in the joint government? Great idea! Mutual defense, technology/expertise collaboration, and economic aid are totally useless anyway!), and political competence.
Oh, and if the Vasudan culture is quite similar to Ubuntu culture, wouldn't it give the Tev leadership pause about beliefs of pacifism/fragility regarding Ubuntu culture? Seeing as vasudan culture is evidently very durable and still quite good on defense?
It's been said the "middle ground" needs to be reached, what exactly would that be?
Since the UEF wants independence, wouldn't "middle ground" involve lessening that independence? What would be acceptable to both the UEF and GTVA?
It's entirely up to the GTVA leadership at this point, which is the problem. They seem to be hell-bent on utterly decimating the UEF's governments, culture, political systems, and any kind of independence. That's kind of approaching unconditional surrender. In other words, the GTVA high command won't settle for anything that's even
remotely "middle ground", and to top it all off, they're the total, sole, and unfettered aggressor in this conflict.
Which kind of infuriates me a bit; this goes beyond ends justifying means, it's downright
impractical and immoral. For one, if Tev culture and political capability is really
that bad, then what makes them think they can wipe out Ubuntu culture and secure the loyalty--politically, culturally, economically, and militarily--after giving every reason for Sol's population to
hate the Tevs? The NTF Rebellion would be
nothing compared to this; if the Fedayeen are any indication, the GTVA can't succeed in truly containing any influence from Sol, and the cause for this rebellion/dissent is
vastly more potent and relatable than NTF ideals. Combine that with the assassination incident, and you've got a potential catastrophe that the Tev leadership seems (or believes itself to be) incapable of effectively preventing.